I. Field of the Invention
The present invention relates to an anaerobic sealant composition employed to seal pipe joints between pin and box members intended for downhole tubular goods used in petroleum drilling operations. The invention encompasses not only the sealant composition itself but the method of its application to the pipe joint structure, and the resulting connection.
For purposes of the invention, the term "petroleum" will be taken to include, but not necessarily be limited to, operations related to the exploration, drilling, and extraction from the earth of oil, gas, water, and geothermal materials as well as the disposal of nuclear and/or toxic wastes. Additionally the term "pipe" will be used for convenience to refer to all downhole tubular goods, whether it be tubing, drill pipe, casing, production pipe, or the like.
The term "drilling", likewise, will be taken to include exploration for and extraction of materials from the earth as well as formation of a deep hole through which the materials are extracted. It will be understood, however, that pipe having the same characteristics of that used in petroleum operations can also be used in the opposite sense, that is, to return materials into the earth. Such a procedure is involved in the return of petroleum products to underground storage or the transfer of nuclear wastes to underground containment fields. Thus the term "drilling", for purposes of the invention, will also include preparation for such storage of petroleum or other products or disposal of nuclear or other wastes beneath the surface of the earth. The invention herein is concerned with the connection between two lengths of pipe. The ends to be joined of the two lengths of pipe are commonly referred to as a "pin" and as a "box". In this context, a "pin" may be an externally or internally threaded end of pipe and a "box" may likewise be an externally or internally threaded end of pipe and a coupling connected thereto with suitable threads for receiving a pin. However, these terms should be read sufficiently broadly to cover connecting mechanisms other than threads. Also, the term "make up" and variations thereof are taken to mean assembly of two pin and box members, and the term "break out" and variations thereof, are taken to mean disassembly of the pin and box members.
II. Description of the Prior Art
The problems associated with petroleum drilling operations are many and extreme. The conditions experienced include extremes in temperature, not only between polar regions and equatorial regions, but also of the products being extracted and the high temperature of the formations at depth. Pressures can be intense in the depths of the earth as well as exposure to the harsh corrosiveness of such toxic materials as sulfur dioxide and hydrogen sulfide.
Particularly grueling are the stresses imposed on downhole tubular goods in the instance of a string of pipe which may be many thousands of feet in length.
Couplings or tubular connections for lengths of pipe are of paramount importance in the drilling operation and serve two primary functions. In the first instance, they hold the weight of the pipe which can amount to two million pounds or more and they serve to seal the pipe both against incursions from its exterior as well as loss of the products being extracted. The customary type of pipe connections used in drilling operations are threaded joints and the industry standards which have been established by the American Petroleum Institute (API) are known as "API 8-round" and as "API buttress" threads.
Leaking pipe connections have represented a significant problem to the petroleum industry, and the problem continues although recent research and development efforts by connection manufacturers and operators have made significant improvements in the technology. Premium connection designs employing various combinations of interference-fit threads metal-to-metal seals, new generation of non-metallic seal materials, higher alloyed steels, and computer/numerical control machining technology have been developed and are very effective. Typical of such premium connection designs are those disclosed in Blose U.S. Pat. No. 4,244,607 issued Jan. 13, 1981 and U.S. Pat. No. Re. 30,647 reissued June 16, 1981. These patents are incorporated in and made a part of this application, by reference, as being typical of the technology relating to premium connections.
Some of these designs include "Teflon" brand o-rings, or the like, as sealing aids. In this instance, sufficient material must be removed from the pipe end in the region of the joint to accommodate the o-ring.
Such removal necessarily weakens the joint and increases the stresses imposed on the joint. Furthermore, the o-ring material does not have sufficient plasticity to satisfactorily seal the interstices of the joint.
Nonetheless, failures continue to occur due in part to greater sensitivity of many of these designs to handling, running, and environmental factors. Single failures of production strings have cost millions of dollars and they continue to occur as industry continues to push back the technology frontier. One of the most pervasive causes of these connection failures is leakage. Aside from design problems, many new connections are easily damaged by a variety of common rig and handling procedures.
As a further effort to prevent leaking connections, sealing materials have been developed and are widely used by the industry. Numerous such sealing materials are available such as Shell high pressure thread compound produced by Shell Oil Corporation, EXXON 706 thread compound produced by EXXON Corporation, and "Liquid-O-Ring" brand thread compound manufactured by Oil Center Research, Inc. of Lafayette, La. These materials meet API standards and are referred to as "API modified". Typically, the components of these sealing materials include an oil based lubricant, and sealant components which may include, for example, powdered graphite, lead powder, zinc dust, and copper flake. There is no chemical reaction between the sealant components and the lubricant. The composition is merely a mixture and there is no curing step involved in its preparation or use. These sealing materials remain in a liquid form, seeking any voids which are present between the mating threads within the joint.
While such sealing materials have worked reasonably well, they are, in composition, primarily a lubricant and only secondarily a sealant. The sealant components of the mixture seek out the voids within the threaded joint, but if a hole is large enough, the sealant material will extrude out and the sealant will no longer be effective for its intended purpose. It also often occurs in the harsh environment in which drilling operations take place that the liquid component of the sealant material bakes off in the extreme heat to which it is exposed, leaving voids and the metallic sealant components behind. These components typically have particle sizes lying in a range of 50 to 500 microns. This is not only undesirable during normal drilling operations, but becomes even more of a problem during disassembly of the pipe. Customarily, the same pipe can be used in a number of reinstallations in the same well or installations in successive wells. This, of course, is desirable because of the heavy expense of the piping. However, in the instance in which the lubricant bakes off, the metallic particles left behind are of a gritty consistency and, upon disassembly, sometimes causes gelling to occur on the threads of the pipe. This causes the pipe to be more difficult to disassemble and severely limits the reuseability of the pipe.